Various types of rotary drill bits, reamers, stabilizers and other downhole tools may be used to form a borehole in the earth. Examples of such rotary drill bits include, but not limited to, fixed cutter drill bits, drag bits, PDC drill bits and matrix drill bits used in drilling oil and gas wells. Cutting action associated with such drill bits generally requires rotation of associated cutting elements into adjacent portions of a downhole formation. Typical drilling action associated with rotary drill bits includes cutting elements which penetrate or crush adjacent formation materials and remove the formation materials using a scraping action. Drilling fluid may also be provided to perform several functions including washing away formation materials and other downhole debris from the bottom of a wellbore, cleaning associated cutting structures and carrying formation cuttings radially outward and then upward to an associated well surface.
A typical design for cutting elements associated with fixed cutter drill bits includes a layer of super hard material or super abrasive material such as a polycrystalline diamond (PDC) layer disposed on a substrate such as tungsten carbide. A wide variety of super hard or super abrasive materials have been used to form such layers on substrates. Such substrates are often formed from cemented tungsten carbide but may be formed from a wide variety of other suitably hard materials. A “super hard layer” or “super abrasive layer” may provide enhanced cutting characteristics and longer downhole drilling life of associated cutting elements.
Backup cutters (sometimes referred to as “secondary cutter”) and/or impact arrestors have previously been used on rotary drill bits in combination with cutting elements having super hard or super abrasive layers. Primary cutters are often disposed on fixed cutter drill bits with respective super hard cutting surfaces oriented generally in the direction of bit rotation. Backup cutters and/or impact arrestors are often used when drilling a wellbore in hard subsurface formations or intermediate strength formations with hard stringers. Backup cutters and/or impact arrestors may extend downhole drilling life of an associated rotary drill bit by increasing both surface area and volume of super hard material or super abrasive material in contact with adjacent portions of a downhole formation. For some applications fixed cutter rotary drill bits have been provided with cutting elements having side cutting surfaces in addition to traditional end cutting surfaces.
Some rotary drill bits with primary cutters oriented to engage adjacent portions of a downhole formation along with secondary cutters trailing the primary cutters and typically oriented to act as impact arrestors often require relatively high rates of penetration before the trailing secondary cutters will contact adjacent portions of a downhole formation. For many drilling operations actual rates of penetration may be lower than this required high rate of penetration. As a result, the trailing secondary cutters or impact arrestors may not contact adjacent portions of the downhole formation. For such drilling operations, the secondary cutters may not effectively control rate of penetration and may not protect the primary cutters.
When prior impact arrestors have been placed in a leading position relative to respective cutters, such impact arrestors have often been able to initially control rate of penetration of an associated drill bit. However, when the cutters become worn, rate of penetration for the same overall set of downhole drilling conditions may increase significantly to greater than desired values.